Thanks for your query.
Once in a while, a woman DOES experience an erratic period.
That said, if you dont have your period by the 11th, then first take a pregnancy test to rule out ectopic pregnancy, pregnancy or a miscarriage.
Next, stress , anxiety, weight loss
, travelling etc could cause this.
Consult a doctor to rule out conditions like hypothyroidism
, raised prolactin levels, polycystic ovaries
, endometrial hyperplasia